1. Field of the Invention
The present invention relates to a robot to assist with the nursing of the elderly and so on, and more particularly to a sensor, and peripheral technology thereof, for detecting the pressure distribution, such as that in multi-jointed arms, and for use in the drive-control of the robot.
2. Description of the Related Art
In an aging society, while nursing of the elderly and so forth is of increasing importance, it is physically demanding for those undertaking the nursing and there are frequent cases of the caregivers themselves sustaining injuries to hips, knees, shoulders, arms and so forth. Such situations have given rise to intensive research and development of means to help with nursing. The advent of nursing robots is also eagerly anticipated but has not yet reached the practical stage. Unlike industrial robots, since such robots are intended for human beings and the physically weak, the movements of such robots must not only be sufficiently safe and reliable, but also delicate, so as to provide those receiving care with a sense of security. In other words, since people require gentle care, the provision of a nursing robot poses tremendous -difficulties in terms of the control and the mechanics involved.
The present inventors initially researched and developed a xe2x80x9cRotary articulated robot and method of control thereofxe2x80x9d, this robot having a construction in which offset joints and rotating joints were integrated, and a Japanese Patent Application was filed (H 11-319334), which corresponds to U.S. patent application Ser. No. 09/708,667. In a multi-jointed robot having a plurality of offset-rotation joints by which the drive-side arm and driven-side arm are rotatably driven about an offset-rotation axis inclined with respect to the arm axis, the multi-jointed robot of this invention is characterized by allowing a hollow rotating shaft to rotate freely, this hollow rotating shaft being inclined by a prescribed offset angle and driven by a motor in the tip of either the drive-side arm or driven-side arm, and characterized by a rotor member being fixed that transmits a rotation force from the abovementioned hollow shaft to the base end of the other arm, and by the abovementioned hollow rotating shaft and abovementioned rotor member constituting a mechanism permitting high deceleration ratio transmission and an increase in torque. With this construction, even smaller drive motors are employed, greater rotational torque can be transmitted, highly precise positioning is possible, and a very lightweight joint with offset rotation at a higher torque is obtained. By virtue of the fact that this offset-rotation joint is linked at many points, it was possible to provide a highly functional multi-jointed robot capable of a wide range of complicated and precise movements with a high payload.
The basic construction of an offset-rotation joint in this multi-jointed robot is shown in FIG. 7. This figure shows the case where the cylindrical hand-base arm is the drive-side arm 6 and the hand-end arm is the driven-side arm 7, and depicts a state in which the driven-side arm 7 is linked by an offset-rotation joint offset by an offset angle y with respect to the arm axis of drive-side arm 6. The tip of the arm main body 6a of drive-side arm 6 is an aperture that is at a night angle to the axis, the base end of the driven-side arm is an aperture that is inclined at an angle of inclination xcex3 with respect to the arm axis, and an offset-rotation joint assembly body is created in the right-rotation joint assembly body in this embodiment is constructed by integrating a motor unit 8, a drive-side arm tip portion 6b fixed to the leading edge of this motor unit, and a joint rotation transmission mechanism 9 fixed to this drive-side arm tip portion. A right-angle aperture is created in the base end side of the drive-side arm tip portion 6b and an inclined aperture is created in the tip side thereof. The right-angle aperture receives the tip of the motor shaft, and the joint rotation transmission mechanism 9 is fixed to the inclined aperture. The motor unit 8 has a motor case 10 of the same diameter as the arm, and by integrating the top and bottom ends of this motor case, as shown in the figure, by linking these ends to the drive-side arm 6a and drive-side arm tip portion 6b, the motor case 10 itself comprises one part of the drive-side arm. The motor unit 8 comprises a motor 11 formed so as to be integral with the abovementioned motor case 10, an encoder E, slip ring 13, and rotation speedometer (not illustrated), and the motor shaft 14 is established in a position on the same axis as the arm axis or on a parallel axis. In a construction of this kind, when the motor 11 is in a driving condition, the cylinder shaft 21 rotates at a prescribed rotational speed via the external teeth bevel gear 17 and internal teeth bevel gear 24. Here, by making the diameter of the internal teeth bevel gear 24 large, the motor is able to decelerate according to the ratio of the gear diameters, and a large torque can be produced using very small motors. Furthermore, it is possible to obtain a large deceleration ratio with a harmonic gear mechanism inside joint rotation transmission mechanism 9, and obtain greater rotational torque using small motors. It is possible, through this rotational torque, to extend the driven-side arm 7 through a desired angle with respect to drive-side arm 6.
The present inventors considered applying the invention xe2x80x9cRotary articulated robot and method of control thereofxe2x80x9d, permitting the provision of a highly functional multi-jointed robot capable of a wide range of complicated and precise movements with a high payload, to the arms of a nursing robot, which pose tremendous difficulties in terms of the control and the mechanics involved because people require gentle care. As far as the arms of the nursing robot are concerned, not only is it essential that the arms be capable of handling the work easily, but the movements of these arms must also not cause a person in care any pain or discomfort. For example, if a movement is considered in which a person lying in bed is picked up by the robot, when particular locations of the robot""s arms are subjected to concentrations of stress, these arms touch the person in care strongly in those locations, and the direct result is that the person is bruised by this strong use of force. Consequently, it is necessary for the arms of the nursing robot to deform and make movements to change to a state in which the person""s body is supported uniformly, and for local concentrations of stress to be avoided. In other words, since it is required for the nursing robot to make movements according to an initial objective, while taking appropriate measures to the state of contact with the person in care, that changes from one moment to the next, it is necessary for the nursing robot to constantly detect the state of holding the person in care and perform control corresponding to this detected value. When attempting to employ the developed multi-jointed robot, developed by the present applicants, as a nursing robot, a sensor, for detecting the state of contact between the robot and the person in care, is of prime importance.
Conventionally, pressure-sensitive sheet sensors have been employed as means for detecting pressure distribution received in particular areas. Such a sensor is shown in FIG. 6 and is formed as a layered single sheet comprising column electrodes 2 arranged on a column electrode side substrate material sheet 1 composed of polyester film or the like, and row electrodes 4 arranged on a row electrode side substrate material sheet 5, a pressure-sensitive resistive raw material 3 being interposed there between. A pressure-sensitive resistive raw material 3 is interposed between specific row electrodes and specific column electrodes of this pressure-sensitive sheet sensor. Consequently, the resistance value between both sets of electrodes depends on the properties of the pressure-sensitive resistive raw material 3 and shows a value in accordance with the stress imparted to areas where both sets of electrodes intersect. Therefore, if resistance values between each row electrode and each column electrode are determined in order, it is possible to detect the pressure in each location of intersection. This pressure-sensitive sheet sensor is capable of detecting the magnitude of the pressure on specific areas that are covered and position information, in other words the pressure distribution received. This pressure-sensitive sheet sensor is employed in the detection of many kinds of pressure distribution such as the determination of the pressure distribution of a body in a bed, the pressure distribution on the surface of a vehicle seat, on a chair seat, on the sole of a foot, and so forth.
The present inventors employed this pressure-sensitive sheet sensor in a multi-jointed robot and tried testing this sensor as a sensor for detecting the state of contact of the nursing robot. However, since the shape adopted for each joint unit of the multi-jointed robot is not that of a simple cylinder, both end portions of which being cut at an offset angle, it is not possible toxe2x80x94detect pressure over the whole surface using a conventional square sheet of matrix electrodes. Further, a nursing robot necessitates real-time, situation-dependant drive control. However, it takes a considerably long time to obtain pressure distribution through operation processing using detected values in a number of locations of intersection between column electrodes and row electrodes, and to perform suitable drive control of each joint based on the contact information resulting from this processing. Consequently, the problem of being unable to achieve the required real-time drive control has become a pressing one.
An object of the present invention is to solve each of the abovementioned problems, in other words the task faced by the present invention is thus to solve the abovementioned problems, that is, to provide a contact sensor capable of determining the pressure distribution over the whole surface of each joint unit, these joint units having a cylindrical shape, both end portions of which are cut at an offset angle, and constituting robot arms, and to provide a technology enabling real-time drive control of the robot arms by using detected values from these sensors.
Therefore, according to the present invention, since the points of intersection of the electrodes are distributed over the whole surface of each joint unit by forming a pressure-sensitive sheet sensor in which column electrodes arranged in parallel and row electrodes arranged in a shape resembling that of wound string, hereinafter referred to as xe2x80x9ca wound-string shape,xe2x80x9d are combined, these joints having a cylindrical shape, both end portions of which are formed as an aperture that is inclined at a prescribed angle and, in addition, since both the column and row electrodes are arranged so as to cover the prescribed width, the number of signal output terminals is reduced and the operation processing load is lightened. Moreover, after executing local processing of signals output from sensors in each of the joints through the use of a processing circuit provided in each of the joints, and sending this data to the central CPU, the total processing speed is raised.